Inkjet heads in which ink is ejected from a plurality of nozzles include a substrate which is formed of a piezoelectric material. The substrate is provided with a plurality of grooves to which ink is supplied. An electrode, to which a driving voltage is applied, is formed on an internal surface of each groove.
Each electrode is covered with a protective film which protects the electrode from ink. For example, an organic film such as polyparaxylene is used as the protective film. The probability that pin holes are generated in an organic film is smaller than the probability that pin holes are generated in an inorganic film. Therefore, even when various types of ink having electrical conductivity are used, it is possible to secure electric insulation of the electrode from ink.
According to inkjet heads of the prior art, the nozzles are formed in a nozzle plate by irradiating the nozzle plate adhered to the substrate with laser light. The laser light is made incident on the inside of the grooves directly after the laser light passes through the nozzle plate, and applied onto the protective film which covers the electrodes.
The organic film which forms the protective film disappears and a hole is generated when the organic film receives laser light, and thus a region of the organic film that receives laser light is damaged. As a result, the electrode is exposed through the hole which is opened in the organic film, and it is difficult to maintain electric insulation of the electrodes from ink. Therefore, in particular, in the case of using ink having electrical conductivity, it is inevitable that the electrodes are melted in an early stage. This reduces the durability of the inkjet head.